1. Technical Field
This disclosure relates to a liquid crystal display device that displays a video picture on a liquid crystal display unit.
2. Description of the Related Art
In a liquid crystal display unit, it is known that, when a direct-current (DC) drive voltage is applied to pixels including liquid crystals in order to drive the pixels, the liquid crystals deteriorate and their life becomes shortened, and the display quality consequently deteriorates. Thus, generally speaking, with a liquid crystal display unit, an alternate-current (AC) voltage drive of inverting the polarity of the voltage applied to the pixels for each frame is performed. In addition, for example, with a dot inversion-type AC voltage drive, the polarity of the voltage applied to the respective adjacent pixels of red (r), green (g), and blue (b) for each frame is inverted alternately for each pixel.
In a liquid crystal display unit to which this kind of AC voltage drive is performed, as shown in FIG. 19 for example, there are cases where a white image and a black image are alternately displayed for each frame. In the foregoing case, since the pixel voltage applied to the pixels relative to a common voltage Vcom becomes a DC voltage Vdc as an effective value, if this continues for a long period, the liquid crystals will deteriorate to thereby cause the display quality to deteriorate. For example, upon displaying an image on a liquid crystal display unit based on an interlaced signal, the alternate display of a white image and a black image tends to occur.
In order to prevent the pixel voltage from becoming the DC voltage Vdc as the effective value, as shown in FIG. 20 for example, a method of inverting the phase of the polarity of the voltage applied to the pixels for each of a plurality of frames is known. Consequently, the bias on the positive electrode side and the negative electrode side of the pixel voltage relative to the common voltage Vcom becomes inverted for each phase inversion. Accordingly, it is possible to inhibit the pixel voltage from becoming a DC voltage as the effective value.
However, as shown in FIG. 21 for example, when an image of substantially the same luminance is displayed, the luminance of the display image will increase in the frame immediately after the phase inversion, and thereby cause a flicker. As shown in FIG. 22 for example, when a phase inversion is not performed, a voltage having a different polarity will constantly be applied to the pixels for each frame. Meanwhile, when the phase of the polarity of the pixel voltage is inverted for each plurality of frames, as shown in FIG. 21, the voltage having the same polarity will be successively applied to the pixels in the frame immediately before the phase inversion and in the frame immediately after the phase inversion. When the voltage having the same polarity is successively applied to the pixels, the response of the liquid crystals will improve in comparison to the other frames. Thus, the luminance of the image in the frame immediately after the phase inversion will increase. Consequently, when performing phase inversion, while it is effective in preventing a DC voltage from being applied to the liquid crystals, there is a problem in that a flicker will occur as a side effect, and the display quality of images will deteriorate. Thus, the technology described in Japanese Patent Application Publication No. 2007-225861 proposes inhibiting the generation of flickers and preventing the deterioration in the display quality of images by lowering the voltage applied to the pixels in the frame immediately after the phase inversion.
However, the deterioration in the display quality of images caused by a flicker is affected by the temperature or variation in the liquid crystal display unit, and it is difficult to completely eliminate such deterioration. Moreover, while the deterioration in the display quality of images caused by a flicker is relatively difficult to detect in moving images such as those displayed on a TV, such deterioration becomes conspicuous in cases where there are many still images and the screen is uniform such as with the images displayed on a personal computer (PC). In recent years, cases of inputting these PC signals into a TV are increasing, and it is necessary to inhibit the generation of flickers and prevent the deterioration in the display quality of images. Meanwhile, since images displayed on PC screens and tablets were mainly based on progressive signals conventionally, this kind of phase inversion itself was not required. However, cases where interlaced signals are input via the internet are increasing. Thus, even with PC screens, it is necessary to prevent the deterioration in the display quality of images while preventing the generation of residual images caused by the application of a DC voltage to the pixels in an interlaced signal.